PKI functions in a Smart Card, e.g. a SIM card localized in a GSM cellular phone, is normally protected by its own PIN code and PUK (Personal Unblocking Code) code (not the same as for the GSM part). The PIN code is normally a relatively short personal number which has to be entered to enable the card for use. The PUK code is normally a much longer number which has to be entered after three times of incorrectly entry of the PIN code. This prevents unauthorized access to the Smart Card.
For security reasons the PUK code must be considerably longer than the PIN code. However, this emerges as a problem for the user because the code is difficult to remember. For most users it is necessary to store the PUK code e.g. on a piece of paper, and on rare occasions, when the PUK code is needed, it may probably be gone. Due to this, mobile telephone operators (or any other type of issuer) frequently have to replace the users Smart Card/SIM. Because of security reasons, it is not a proper handling to reprint a PUK twice. This will imply extra cost and work to renew the subscription with a new PUK and a Smart Card as well.
The PUK code is a fixed code, thus requiring storage of the code locally in the Smart Card. An additional problem due to the fact that the PUK code is a fixed code, is that the Smart Card is tied up to one user during its life time, and there is no possibility for changing the user for a certain subscription. This implies manufacturing and distribution of more Smart Card than necessary.